The present invention relates to a metal mold arrangement for producing a cylinder block of an internal combustion engine, and more particularly to a type thereof having separate cores.
For cooling an internal combustion engine, a cylinder block is formed with a water jacket surrounding a plurality of cylinder liners juxtaposedly arranged with each other. Further, a closed deck type cylinder block has been provided in which bridge portions are provided to partly cover an open end of the water jacket at a top deck side of the cylinder block in order to reduce vibration of the engine and to reinforce the cylinder block. A crank case is provided at a side opposite the top deck.
For casting the cylinder block, a metal mold is provided whose internal configuration is coincident with an external shape of the cylinder block, and a water jacket die is positioned within the metal mold. Further, a protruding die is positioned within the water jacket die for defining a cylinder bore. A water jacket appears upon pulling out the water jacket die after solidification of a molten metal. Because the bridge portions are provided at the top deck side upon casting, it is necessary to place separate cores at positions corresponding to the bridge portions in order to allow the water jacket die to be pulled out from the casted product.
Japanese Patent Application Kokai No. Hei-9-70645 discloses a water jacket die formed with a plurality of recessed portions each extending in an axial direction of a cylinder liner. Separate cores each fittable with each recessed portion are provided for forming bridge portions. The separate cores are solid structure and are formed from ferrous material. Each separate core is subdivided into two pieces whose parting faces extend in the axial direction of the cylinder liner. The subdivided two pieces have upper and lower surfaces slanted into generally V-shape such that a distance between the upper and lower surfaces is gradually increased toward a direction away from the parting faces in the circumferential direction of the water jacket in order to provide a draft or a slope. Further, each subdivided two piece has a thickness in a radial direction of the cylinder liner, the thickness being gradually increased toward a direction away from the parting face in the circumferential direction in order to provide a slide draft or slope.
At each bottom of each recessed portion of the water jacket die, a projection is provided for forming an opening in an ultimate cylinder block. Therefore, when each separate core is fitted in each recessed portion, the lower surface of the separate core is mounted on the projection in such a manner that the parting faces of the subdivided pieces are in alignment with the projection. Because of the provision of the projection, a space is defined between the lower surface of the separate core and the bottom surface of the recessed portion, so that the molten metal can be filled in the space to provide the bridge.
After opening the metal mold, the water jacket die is pulled out from the casted product remaining the separate cores within the water jacket. A bore is formed in each bridge portion at a position corresponding to the projection. By inserting a jig through the bore, the two subdivided pieces of the separate core are pushed and moved away from each other, so that the separated subdivided pieces are pivotally moved about each lower corner. Accordingly, each upper surface of the subdivided pieces can be offset from the bridge portion. Thus, the subdivided pieces can be removed from the cylinder block through the upper open end of the water jacket.
In the water jacket die according to the Japanese Patent Application Kokai No.Hei-9-70645, each separate core can be easily removed from the water jacket by pivotally moving the subdivided pieces in a direction away from each other upon insertion of the jig and pushing the jig onto the parting faces of the subdivided pieces. Further, because the separate cores are formed by the solid metallic material, the separate core can be produced easily and can withstand casting pressure.
However, due to the subdivided construction, it would be rather difficult to set the separate core at a given position, and precise clearance is required between the separate core and the metal mold. Thus, high dimensional accuracy is required in the separate cores and the water jacket dies. Particularly, in order to remove the separate cores from the water jacket, the subdivided pieces are moved away from each other in the water jacket and in a direction away from the bridge portions. Consequently, a proper dimensional relationship is required between a size of the subdivided pieces and a thickness (a length in a radial direction of the cylinder) of the water jacket at the moving area of the subdivided pieces, otherwise the subdivided pieces cannot be removed out of the water jacket. In this respect, the water jacket die must provide high dimensional accuracy. Moreover, a metal penetration may occur at a contact surface between the separate cores and the metal mold, which in turn generate burrs. Thus, a work for removing the burrs from the metal mold is required, which lowers productivity. In particular, since the parting faces between the subdivided pieces are positioned immediately below the casted bridge portion, burr removal work becomes difficult due to the existence of the bridge portion. Further, since the bore is formed in the bridge portion, mechanical strength of the bridge portion may be lowered. Furthermore, the jig must be required which must be properly sized to be insertable through the bore.
Japanese Patent Publication No.Hei7-108449 discloses a hollow metallic separate core fittable in a recessed portion of a water jacket die in order to form a bridge portion at a top deck of a cylinder block. After the bridge portion is casted at the top deck side, the water jacket die is pulled out of the water jacket while the separate core remains in the water jacket. In this case, vertical side faces of the separate core extend in an axial direction of the cylinder and are positioned offset from the bridge portion. Thus, a drilling machine is accessible to the vertical side faces. By removing the vertical side faces by the drilling machine, the water jacket can be entirely fluidly connected around the cylinder liners because the separate core are hollow construction. If high casting pressure is applied, sand can be filled in the hollow separate core in order to increase strength of the core. In the latter case, the sand can be discharged out of the water jacket upon removal of the vertical side faces of the separate core.
However, according to the method for producing the cylinder block disclosed in the Japanese Patent Publication No.Hei7-108449, drilling work is required for removing the vertical side faces of the separate core after casting in order to provide a complete fluid communication in the water jacket. This work requires skill. Further, a production of the separate core is rather difficult due to the hollow structure. Furthermore, sand must be filled in the hollow separate core in case of the casting at a high casting pressure. In the latter case, sand discharging work must be required to lower the productivity.
It is therefore an object of the present invention to provide an improved metal mold arrangement for producing a cylinder block of an internal combustion engine, the arrangement being capable of facilitating setting of each separate core into a metal mold and facilitating removal of each separate core from the water jacket.
Another object of the invention is to provide such metal mold arrangement in which a design of a water jacket die is not subjected to severe requirement, and burr occurring portions can be reduced, and burr removal work can be easily performed.
Still another object of the invention is to provide such metal mold arrangement capable of providing a relatively large area of bridge portions and facilitating production of the separate cores.
These and other objects of the present invention will be attained by an improved metal mold arrangement for producing a closed deck type cylinder block made from an aluminum alloy. The cylinder block has a plurality of cylinder bores juxtaposed with each other to form a cylinder array and is formed with a water jacket surrounding the cylinder array. The cylinder block also has a top deck at which one end of the water jacket is defined as an open end, a plurality of bridge portions partly covering the open end, and a crankcase side end face opposite the top deck. The metal mold arrangement including a cylinder block forming die and a plurality of separate cores. The cylinder block forming die includes at least a first wall portion defining a configuration of the top deck, a cylindrical protruding sections for defining an inner configuration of the cylinder block, a second wall portion defining a configuration of the crankcase side face, and a water jacket die portion positioned to surround the cylindrical protruding sections for defining a configuration of the water jacket. The water jacket die portion is formed with a plurality of recesses extending in an axial direction of the cylinder bores and opening at the crankcase side face. Each recess is a rectangular shape having a pair of side wall surfaces, an opening positioned at the crankcase side face, and a bottom wall surface opposite the opening. The bottom wall surface extends in a direction intersecting with the axial direction and is oblique to a direction of the array of the cylinders. The bottom surface is partly open to the first wall portion. Each of the plurality of separate cores has a solid structure and is made from a metal and has a rectangular shape complementary with each recess. Each single one of the separate cores is insertable into each recess in the axial direction from its opening. Each separate core has a top deck side slant end face serving as a first draft and a crankcase side slant end face serving as a second draft. The top deck side face and the crankcase side face are slanted in opposite direction against each other such that a distance between the top deck side slant end face and the crankcase side slant end face in the axial direction of the cylinder is gradually increased in a circumferential direction of the cylinder. An inclination of the bottom wall surface of each recess is coincident with an inclination of the top deck side slant end face.
According to the metal mold arrangement of the present invention, setting of the separate core in the metal mold can be facilitated because not subdivided two pieces but a single separate core is to be positioned in each recessed portion. Further, an area of each bridge portion can be increased to enhance mechanical strength because formation of a hole in each bridge portion is not required. Furthermore, it is unnecessary to prepare and use a special jig to be inserted into the hole. Further, since only a single separate core is required for the corresponding recessed portion, merely moving the separate core within the water jacket space toward the neighboring cylinder can remove the core from the cylinder block. In other words, a simple design for the water jacket die portion can result. This is in high contrast to the arrangement in JP Hei9-70645 in which subdivided pieces must be moved in opposite directions, so that special care is required in the water jacket space design for allowing the subdivided pieces to be moved in the opposite directions. Further, the single separate core does not provide therein a parting face. Accordingly, burr generating portion can be reduced, and easy burr removal work can result. Further, since the separate core is of a solid structure, such a core can sustain high casting pressure without any deformation, and the core can be produced easily in comparison with a separate core of a hollow structure.